The conductances of sodium hydroxide solutions at 15�, 25�, 50�, and 75� have been determined at concentrations up to 0.02N with special precautions to eliminate the effects of carbon dioxide and of alkaline attack on glass cells. The limiting conductances have been determined from the Fuoss-Onsager and Pitts equations, and the mobility of the hydroxide ion calculated. The theoretical specific conductance of water at various temperatures has been calculated.